10.11.3 Calibration models

To validate candidate RR Lyrae stars provided by the Classifiers and infer their pulsation mode, the SOS Cep&RRL pipeline uses tools such as the period-amplitude (PA) diagram computed in the $G$ band and diagnostics such as the parameters of the Fourier decomposition of the $G$-band light curve (${\varphi }_{21}$ vs $P$ and ${\varphi }_{31}$ vs $P$ diagrams), as described in the articles on the processing of RR Lyrae stars released in Gaia DR1 and DR2 (see details in Clementini et al. 2016, 2019). The pipeline also estimates the metallicity $[\mathrm{Fe}/\mathrm{H}]$ of RR Lyrae stars from the ${\varphi }_{31}$ parameter of the Fourier decomposition of the $G$-band light curve and individual interstellar absorption values in the $G$-band for fundamental mode RR Lyrae stars (RRab), from a relation based on the star $G$-band peak-to-peak amplitude and the pulsation period (Piersimoni et al. 2002).